Anticathodes for X-ray tubes



Ju 9, 1964 R. KIEFFER ETAL 3,136,907

I ANTICATHODES FOR X-RAY TUBES Filed Jan. 5,1961

INVENTORS AW 664/4 0 K/FFFE/P BY X/I/PL 5501475095? United States PatentM 3,136,907 ANTICATHODES FOR X-RAY TUBES Richard Kiefier and KarlSedlatschek, Reutte, Tirol, Austria, assignors to Metfllwerk PlanseeAktiengesellschaft, Tirol, Austria, a corporation of Austria Filed Jan.5, 1961, Ser. No. 81,216 4 Claims. (Cl. 313-55) This invention relatesto X-ray or Roentgen tubes which operate with fixed or rotary anodes foruse in medical applications, determining the crystal structure ofvarious substances, and other services. Such X-ray tubes operate as arule with an anticathode or anode of pure tungsten. There are manyapplications wherein it is of utmost importance to operate such X-raytubes with a very high load factor. However, the level of the loadfactor to which such X-ray tubes may be subjected is limited by the factthat the beam-impinged target area of the tungsten cathode developscracks because of high thermal loading thereof, thereby making itimpossible to increase the anticathode load of such tube above a limitedlevel.

Among the objects of the invention is an X-ray tube which will permitloading of its anticathode by the electron beam to a materially higherextent than heretofore possible. In accordance with the invention, theanticathode or anode of X-ray tubes which are to be subjected to highelectron-beam load, are provided at least in the region of theirelectron-beam target area, with a target-area layer formed of an alloyconsisting of 10% to 35% rhenium and as balance the base metal tungsten.

. (Throughout the specification and claims, all proportions are given byweight unless otherwise specifically stated.)

The foregoing and other objects of the invention will best be understoodfrom thefollowing description of exemplifications thereof referencebeing had to the accompanying drawings wherein FIG. 1 is a partiallydiagrammatic elevational view of an X-ray tube having a rotary anodeexemplifying the invention; and

FIG. 2 is a partially cross-sectional and partially elevational view ofthe bottom part of the anode of FIG. 1 on a greatly enlarged scale.

FIGS. 1 and 2 show partially diagrammatically an example of an X-raytube operating with a rotary anode exemplifying theinvention. A glassenvelope 1 contains in its highly evacuated interior space a cathodestructure 2 carrying filament 3 and an electron concentrating element 4located opposite a narrow portion of the conical target layer 5 ofrotary anode disk 6. The anode disk 6 has central anode shaft 7 which isrotated by a motor 8.

Under application of high tension voltage a concentrated electron beamemitted by the negative cathode filament 3 will bombard a facing portionof the positive anode target area 5 and cause it to emit X-rays. Theenergy of the electron beam impinging upon the anode target area 5 istransformed almost entirely into heat which is transmitted to and heatsthe entire mass of the anode 6. Under excessive heat the metal of thetarget area 5 of anode6 develops cracks which reduce the X-ray emissiontherefrom.

In accordance with the invention at least the target surface layer 5 ofthe anti cathode or anode 6 of the X-ray tube is formed of an alloyconsisting of 10% to 25% of rhenium and as balance of a base metalalloyed with the 3,136,907 Patented. June 9, 1964 rhenium and selectedfrom the group consisting of tungsten alloyed with up to 14% of tantalumor niobium or a mixture of tantalum and niobium. Furthermore, suchrhenium alloyed target layer 5 of the anode should be at least aboutinch thick.

For best results, at least the target surface layer of the anticathodeor anode of the X-ray tube, consists of 10% to 25% rhenium, and asbalance the base metal tungsten. It has also been found that the basemetal of such anticathode or anode of the invention may be formed of analloy of tungsten with one or more of the metals of the group consistingof niobium and tantalum, thereby yielding a target anticathode bodyformed of a ternary alloy, such as consisting of tungsten, 10% tantalum,and 30% rhenium, which case, the base metal consists of about 86%tungsten and 14% of tantalum. The entire anticathode or anode of anX-ray tube may be formed of such alloys of tungsten with rhenium, orsuch tungsten alloys with rhenium. Since rhenium is scarce and costly,only a surface layer of the anticathode which constitutes the target forthe electron beams, is formed of such basemetal rhenium alloy, thebalance of the anticathode being formed of the base metal tungsten.

Anticathodes for X-ray tubes of the invention may be formed by mixingpowder particles of tungsten and rhenium in the specified proportions,and compacting such metal-powder mixture in a die cavity having theshape of the anticathode, followed by sintering and forging of thesintered metal powder body to give it high density and the desired finalshape. For producing an anticathode or anode for an X-ray tube whereinonly the target area layer of the anticathode is formed of the rheniumbasemetal alloy, a layer section of the die cavity in which theanticathode is to be formed, for instance ,4 in thickness, is filledwith the alloy powder mixture consisting of rhenium particles andbase-metal particles in the abovespecified proportions, with the balanceof the die-cavity filled with the base metal only. After so compactingthe powder body in the die into a green, self-supporting compact, it issintered, for instance under protective atmosphere or under vacuum, attemperatures in the range between 2300 C. and 2800 0., followed byforging or coining to final shape at a temperature range between 1400 C.and 1600 C. FIG. 2 shows in partial crosssection an example of suchX-ray anode 6 of the invention.

The main body of the anode disk 6 is made of a refractory metal such astungsten or an alloy of tungsten with tantalum and/or niobium, asdescribed above. To increase its load factor the anode target layer 5 isat least A inch thick and consists of 10% to 25% rhenium alloyed withthe base metal thereof consisting of tungsten or tungsten alloyed withup to 14% of tantalum and/ or niobium. Rhenium being scarce, only thetarget layer 5 of the anode 6 is shown formed of the rhenium containingbase metal alloy.

It will be apparent to those skilled in the art that the novelprinciples of the invention disclosed herein in connection with specificexemplifications thereof, will suggest various other modifications andapplications of the same. It is accordingly desired that in construingthe breadth of the appended claims, they shall not be limited to thespecific exemplifications of the invention described above.

We claim:

1. In an X-ray tube, the combination of a metallic anode having anexposed target area and beam means including an electron source forproducing an electron beam impinging on said exposed target area andcausing said exposed target area to emit X-rays,

a metal layer of said anode having said exposed target area and being atleast about of an inch thick consisting essentially of 10% to 25%rhenium and as balance of a base metal alloyed with said rhenium, saidbase metal being selected from the group consisting of tungsten,tungsten alloyed with up to 14% tantalum, tungsten alloyed with upto 14%niobium and tungsten alloyed with up to 14% of tantalum and niobium. a

2. In an X-ray tube as claimed in claim 1, said base metal consistingessentially of tungsten.

3. In an X-ray tube as claimed in claim 1, said metal alloy containing5% to 25 of Re, said base metal consisting essentially of tungsten, bodyparts of said anode other than said surface layer consisting essentiallyof tungsten.

4. In antX-ray tube as claimed in claim 1, said base metal consistingessentially of tungsten, body parts of said anticathode other than saidsurface layer consisting essentially of tungsten alloyed with tantalum.

References Cited in the file of this patent UNITED STATES PATENTS2,863,083 Schram Dec. 2, 1915 8

1. IN AN X-RAY TUBE, THE COMBINATION OF A MEALLIC ANODE HAVING AN EXPOSED TARGET AREA AND BEAM MEANS INCLUDING AN ELECTRON SOURCE FOR PRODUCING AN ELECTRON BEAM IMPINGING ON SAID EXPOSED TARGET AREA AND CAUSING SAID EXPOSED TARGBET AREA TO EMIT X-RAYS, A METAL LAYER OF SAID HAVING SAID EXPOSED TARGET AREA AND BEING AT LEAST ABOUT 1/18 OF AN INCH THICK CONSISTING ESSENTIALLY OF 10% TO 25% RHENIUM AND AS BALANCE OF A BASE METAL ALLOYED WITH SAID RHENIUM, SAID BASE METAL BEING SELECTED FROM THE GROUP CONSISTING OF TUNGSTEN, TUNGSTEN ALLOYED WITH UP TO 14% TANTALUM, TUNGSTEN ALLOYED WITH UP TO 14% NIOBIUM AND TUNGSTEN ALLOYED WITH UP TO 14% OF TANTALUM AND NIOBIUM. 